Splashguard and inlet diffuser for high vacuum, high flow bubbler vessel

ABSTRACT

The present invention is a bubbler having a diptube inlet ending in a bubble size reducing outlet and at least one baffle disc positioned between the outlet of the diptube and the outlet of the bubbler to provide a narrow annular space between the baffle disc and the wall of the bubbler to prevent liquid droplets from entering the outlet to the bubbler. The bubble size reducing outlet is an elongated cylindrical porous metal frit situated in a sump of approximately the same dimensions. A metal frit is placed at the inlet of the outlet of the bubbler. The present invention is also a process of delivering a chemical precursor from a bubbler vessel having the above structure.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. Provisional PatentApplications 60/875,200 filed Dec. 15, 2006 and 60/908,376 filed Mar.27, 2007.

BACKGROUND OF THE INVENTION

The electronics fabrication industry uses chemical precursor containersthat convert liquid chemicals into chemical vapor for delivery toelectronics fabrication reactors, i.e. tools, for conducting chemicalvapor deposition (“CVD”). CVD is a favored technique for forming layers,films and other depositions in the construction of electronicfabrications such as integrated circuits or computer chips. Liquids orsolids are preferred as sources of supply because of the efficiency oftransport and storage of a volume of chemical precursor, but theindustry frequently prefers to actually deliver the chemical precursorat the site of the tool in the form of a vapor, i.e. CVD. Alternatively,some fabrications are conducted using direct liquid injection (“DLI”),although even then, the liquid is vaporized in the tool after delivery.

When using vapor delivery for CVD, the containers typically have aninert carrier gas passed through them or bubbled, i.e., bubbler, tocarry entrained chemical precursor vapor in the inert carrier gas to thetool. Bubblers typically have a downtube inlet where the carrier gas isintroduced into the container under the surface of the liquid chemicalprecursor wherein the carrier gas bubbles up through the liquid chemicalprecursor, entraining the chemical precursor as the carrier gas surfacesthe liquid as a bubble and exits the container or bubbler by an outletset above the liquid level of the chemical precursor.

It is undesirable to have the chemical precursor leave the containerthrough the outlet in the liquid form, even as small droplets. Ahomogenous vapor is preferred as the dispensed product of such bubblers.This avoids corrosion, cleanup, and uneven flow, especially through massflow controllers which control the flow of chemical precursor from thebubbler to the tool in a precisely metered fashion.

The industry has attempted various forms of splashguards for bubblers toaddress this issue, such as in: U.S. Pat. No. 6,520,218; EP 1 329 540;US 2004/0013577; EP 0 420 596; U.S. Pat. No. 5,589,110; U.S. Pat. No.7,077,388; US 2003/0042630; U.S. Pat. No. 5,776,255; and U.S. Pat. No.4,450,118. Each of these attempts to provide splashguard function hashad less than desired performance, but the present invention asdisclosed below successfully provides high levels of splashguardfunction, while still allowing high flows of chemical precursor or flowsunder high vacuum or high pressure differential conditions as will bedescribed and illustrated below.

BRIEF SUMMARY OF THE INVENTION

The present invention is a bubbler having a diptube inlet ending in abubble size reducing outlet and at least one baffle disc positionedbetween the outlet of the diptube and the outlet of the bubblerconfigured to provide a narrow annular space between the baffle disc andthe inside wall of the bubbler capable of preventing liquid dropletsfrom entering the outlet to the bubbler. The bubble size reducing outletis a tubular porous diffuser situated in a sump in the floor or bottomof the bubbler container wherein the sump is shaped to the approximatesize and shape of the diffuser with sufficient tolerance to allowbubbles to escape the diffuser and liquid product to surround thediffuser in the sump.

The present invention is also a process of delivering a chemicalprecursor from a bubbler vessel comprising; passing a carrier gasthrough a diptube of a bubbler and further through a bubble sizereducing outlet, such as a diffuser in a sump; entraining liquidchemical precursor from the bubbler into the carrier gas; passing theentrained chemical precursor and carrier gas past at least one baffledisc in a narrow annular space between the outer perimeter of the baffledisc and the inner surface of bubbler sidewall.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic side view of a first embodiment of the presentinvention.

FIG. 2 is a schematic side view of a second embodiment of the presentinvention.

FIG. 3 is a detailed schematic side view of the second embodiment of thepresent invention of FIG. 2.

FIG. 4 is a detailed schematic side view of the inner functionstructures of the second embodiment of the present invention of FIG. 3.

FIG. 5 is a detailed schematic side view of the inner functionstructures of the second embodiment of the present invention of FIG. 2showing a diffuser in a sump configured to the approximate shape of thediffuser.

FIG. 6 is a detailed schematic side view of the inner functionstructures of FIG. 5 showing an alternate elbow outlet 34.

FIG. 7 is a detailed schematic side view of the inner functionstructures of FIG. 5 showing an alternate “Tee” outlet 36.

FIG. 8 is a detailed schematic side view of the inner functionstructures of FIG. 4 showing an alternate embodiment where baffle disc22 has perforations 38.

FIG. 9 is a detailed schematic side view of the inner functionstructures of FIG. 4 showing an alternate embodiment where baffle disc24 is constructed of a porous metal frit material.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a vapor generation bubbler designed for servicein high vacuum or high flowrate conditions. The design preventssplashing and transport of aerosol droplets into the outlet deliveryline that would result in erratic chemical mass flow delivery.

Semiconductor manufacturers are turning to the use of high valuechemicals that are increasingly difficult to transport for depositiononto a wafer in a vacuum chamber or tool. The vessel or bubbler of thepresent invention allows liquid chemical to be delivered from thecontainer or bubbler as a vapor at high vacuum, without the splashingand the formation of aerosol droplets in the outlet of the vessel orbubbler that result in erratic chemical mass delivery rate. The presentinvention has a lower surface design that enables a constant saturationof a carrier gas with chemical vapor down to very low levels of theresidual chemical. Yet, the present invention prevents splashing and theformation of aerosol droplets into the outlet of the bubbler, that wouldresult in erratic chemical mass delivery rate, even when the chemicallevel in the container is high. Previously, bubblers used for highvacuum service or high flowrate service had to be used with only apartial charge of chemical (i.e.: 50% full). This required thesemiconductor manufacturer to change the vessel or bubbler more often(taking down the tool), and added to the cost of the chemical, becauseof the increased container processing fees. This invention enables useof the bubbler from a full liquid chemical level down to a very lowlevel and reduces semiconductor tool downtime. Also, since it iseffective at limiting the chemical aerosol particles in the outlet, itcan reduce particulate generation that might result from degradation ofthe aerosol droplets that deposit in the outlet and all of the deliverypiping to the processing chamber or tool.

Previous bubbler designs addressed the problem of splashing byinstalling at the bottom of the dip tube, piping, perpendicular to thediptube, with holes drilled along its length. This resulted in smallerbubbles generated over a larger area of the bubbler, which resulted in aless turbulent bubbling action, and therefore, less splashing, but theseinventions are impossible to effectively clean for reuse by the chemicalsupplier.

The present invention uses porous masses of material, such as porousmetal frits, at the outlet of the inlet diptube to break down the sizeof the bubbles of inert carrier gas entering the liquid chemicalprecursor in conjunction with one or more baffle discs at the upper partof the vessel or bubbler that requires the carrier gas entrained withchemical precursor to pass indirectly to the outlet of the container orbubbler by flowing tortuously to the outside of the baffle discs in anarrow annular space between the inner diameter of the bubbler insidewall and the outer diameter or circumferential or perimeter edge of thebaffle discs. This will be illustrated with reference to severalpreferred embodiments of the present invention.

FIG. 1 shows a bubbler 10 of the present invention having a cylindricalbubbler sidewall 12 with a diptube inlet 14 terminating at its inlet endwith a porous mass or block outlet, such as a stainless steel frit 18that operates as a gas diffuser to generate small microbubbles of theinert carrier gas below the surface of the liquid chemical precursor(not illustrated). This reduces the chance of violent bubbling or thesplattering of liquid above the headspace or freeboard of the bubbler.The outlet 18 of the bubbler diptube inlet 14 is proximate the floor ofthe bubbler in a sump 21, shown in FIG. 5.

In addition, the diptube 14 has a baffle disc 20, having a circular andconcave downward configuration like a shallow cone opening downward,affixed, as by welding, to the upper end of the diptube 14, to furtheravoid liquid splattering or large scale liquid entrainment of thecarrier gas flowing to the outlet 16, which is undesired, but which hasa greater probability under high flow or high vacuum conditions.

FIG. 2 shows a second embodiment of the present invention where similarparts have similar part numbers. Here the splash guard comprises twobaffle discs, a lower baffle disc 22 and an upper baffle disc 24 havinga circular outer edge shape and being concave downward, such as ashallow downwardly open cone, that act in cooperation to make an evenmore tortuous path for chemical precursor leaving the bubbler 10. Thebaffle discs are concave downward to further frustrate direct flow ofchemical precursor to the outlet 16 and to collect condensed chemicalprecursor for return by coalesced droplets falling back into the storedchemical precursor (not illustrated). The baffle discs have a diameterslightly less than the inside diameter of the cylindrical inside wall ofthe bubbler. The space between the circumferential or perimeter edge ofthe baffle disc and the inside wall of the bubbler is sufficient toallow gas to pass through the space with minimal pressure drop, butsufficiently narrow to minimize the passage of liquid that may beejected from the liquid content of the bubbler under high flow rates ofcarrier gas through the diptube or significant pressure fluctuations.

FIG. 3 shows a more detailed illustration of the second embodiment ofthe present invention. Bubbler 10 is shown in cut away with an angleddiptube 14 ending in a stainless steel frit outlet 18, such as a Mottporous stainless steel cup Series 1200, catalog no 1200-A-B-L-Mediagrade. The two baffle discs 22 and 24 occupy different inside diameterlocations in the container sidewall 12 so that the lower baffle disc 22allows greater annular space from the cylindrical inside surface of thebubbler sidewall 12 for carrier gas and chemical precursor to passtoward the outlet, while upper baffle disc 24 provides less annularspace to further avoid liquid entrainment in the outlet and downstreampiping from the outlet.

FIG. 4 shows an isolation of the internal structure of the bubbler ofthe second embodiment without the sidewall 12 being illustrated. In FIG.4, the diptube inlet 14 and its outlet frit 18 are easily seen and thesplash guard comprising baffle disc 22 and 24 are also readily seen withtheir concave downward shape.

FIG. 5 shows a specific configuration of the second embodiment of FIG. 2in which the gas diffuser outlet 18 is shown as an horizontally disposedelongated cylindrical porous metal frit having a hollow gas passageinterior and a porous metal frit outer shell, such as those made by MottCorporation, Farmington, Conn. 06032, USA. Preferably, the porous metalfrit gas diffuser outlet 18 has a media grade rating to filter outparticles of 1 micron or larger, preferably filtering out at least 90%of particles 1 micron or larger.

The gas diffuser outlet 18 of FIG. 5 is situated in a sump 21 in thebase, floor or bottom of the bubbler container 12. The preferreddiffuser 18 is an horizontally disposed elongated cylinder and the sumpis thus a partial elongated cylinder open at its upper side to theinside of the bubbler and being of a dimension slightly larger than theelongated cylinder of the diffuser outlet 18, sufficient to allow gasbubbles of carrier gas to escape the outside of the diffuser outlet 18and to allow liquid chemical precursor stored in the bubbler or vessel10 to reside in the sump 21 substantially or completely surrounding thediffuser outlet 18. Preferably, the diffuser outlet 18 resides entirelywith the sump 21, such that the upper surface of the diffuser is no morethan even with the upper edge of the sump wall. The level sensor 28measures the liquid product level. Inlet 14 is controlled by inlet valve30, and outlet 16 is controlled by valve 26. The goal of FIG. 5 is toprovide adequate flow of gas to entrain liquid product without creatingbubbles of such size as to create splashing or violent spitting of theliquid getting to the outlet and downstream of the bubbler. This couldcontaminate the outlet or create flow problems in any downstream massflow controller. To further avoid liquid escape from the bubbler, ametal frit 32 can be positioned at an inlet to the outlet 16.

FIG. 6 shows the embodiment of FIG. 5 in which an elbow configuration orshape 34 of the inlet to the outlet 16 is used in place of metal frit32. The end of elbow 34 is directed radially inward away from the outercircumferential or perimeter edge of the baffle discs 22 and 24 andtoward the axial center of the cylinder formed by the sidewall 12 of thevessel or bubbler 10 to minimize possible liquid introduction into theoutlet 16.

Similarly, FIG. 7 shows an alternate to FIG. 6 wherein the elbow outlet34 is replaced with a “Tee” shaped or configured inlet 36 to the outlet,again to minimize the possible introduction of liquid into the outlet 16from the annular space between the baffle discs 22 and 24 and the insidewall of the sidewall 12 of the vessel or bubbler 10.

To avoid liquid introduction into the outlet 16, it is further possibleto change the construction of the baffle discs. FIG. 8 shows lowerbaffle disc 22 with a plurality of perforations 38 to trap liquidspitting between baffle discs 22 and 24 and return it to the sump of thevessel. FIG. 9 shows that upper baffle disc 24 is fabricated from porousmetal frit material, to again minimize liquid introduction into theoutlet 16.

The present invention provides superior minimization of liquidentrainment of droplets in the outlet and downstream piping of a bubblerconnected to a CVD tool of an electronics fabrication system. Usingeither a single baffle disc or multiples of the baffle disc, alone or incombination with a diffuser or frit at an outlet to the diptube inletprovides the desired minimization of liquid droplet entrainment in theoutlet 16 of the bubbler.

Although the baffle discs have been shown as circular discs with aconcavity where the disc is slightly smaller than the inside diameter ofthe cylindrical vessel or bubbler sidewall, it is understood that anybaffle of any shape which provides only a narrow annular space at theinner sidewall of the vessel or bubbler is within the scope of thepresent invention. Likewise, any form of device with an array of smallpassages can be used as the frit or outlet of the diptube of the presentinvention.

Although, it is preferred to use stainless steel, it is envisioned thatany inert material of rigid form can be used for the splash guard orfrit. Plastics, metal alloys, powdered metals, fabrics, textiles andceramics are all contemplated.

The vessel 10 can also be used for product flow in the oppositedirection where outlet 16 functions as a pressurizing gas inlet to forma pressure head on liquid contained in the vessel 10 and force theliquid in liquid form through the frit 18 and out the diptube 14 forliquid delivery from the vessel using a pressurizing gas, in contrast tothe vapor delivery described above.

The invention claimed is:
 1. A bubbler for storing a volatile liquidchemical and delivering vapor of the volatile liquid chemical to a vapordeposition process when under vacuum, the bubbler comprising acylindrical inside wall having a diameter, a floor, a diptube inletending in an outlet proximate the floor and at least one baffle discaffixed to an upper end of the diptube and positioned between the outletof the diptube and an outlet of the bubbler, wherein the at least onebaffle disc has a circumferential edge and a diameter slightly less thanthe diameter of the inside wall such that the space between thecircumferential edge of the baffle disc and the cylindrical inside wallis sufficient to allow the vapor of the volatile liquid to pass throughthe space with minimum pressure drop, but sufficiently narrow tominimize the passage of liquid that may be ejected from a volatileliquid content under vacuum conditions and high flow rates of a carriergas through the diptube, wherein the at least one baffle disc is solidand has a concave downward shape to collect condensed volatile liquidchemical for return by coalesced droplets that fall back into the storedvolatile liquid chemical, wherein in operation under vacuum conditions,the bubbler is capable of preventing liquid droplets from entering theoutlet of the bubbler.
 2. The bubbler of claim 1 wherein the outlet is abubble size reducing outlet.
 3. The bubbler of claim 2 wherein thebubble size reducing outlet comprises a porous metal frit.
 4. Thebubbler of claim 3 wherein the porous metal frit has porosity to filterout particles of 1 micron or larger.
 5. The bubbler of claim 4 whereinthe porous metal frit has porosity to filter out greater than 90% ofparticles of 1 micron or larger.
 6. The bubbler of claim 1 wherein aninlet to the outlet of the bubbler comprises a porous frit to minimizeliquid entering the outlet of the bubbler.
 7. The bubbler of claim 1wherein an inlet to the outlet of the bubbler comprises an elbowconfiguration to minimize liquid entering the outlet to the bubbler. 8.The bubbler of claim 1 wherein an inlet to the outlet of the bubblercomprises a “Tee” configuration to minimize liquid entering the outletof the bubbler.
 9. The bubbler of claim 1 having at least two bafflediscs comprising an upper baffle disc and a lower baffle disc.
 10. Acylindrical vapor generation bubbler vessel having a diptube inletending in an outlet for delivering a carrier gas into the bubbler vesseland two baffle discs affixed to an upper end of the diptube, wherein thebaffle discs have a circular and concave downward shape, the bafflediscs comprising an upper baffle disc and a lower baffle disc, whereinthe upper baffle disc and the lower baffle disc are positioned betweenthe outlet of the diptube inlet and an outlet of the bubbler vesselconfigured to provide a narrow annular space between an outercircumferential perimeter edge of the baffle discs and the inside wallof the bubbler vessel, wherein the narrow annular space is capable ofminimizing liquid droplets from entering the outlet to the bubblervessel when the carrier gas is bubbled through a liquid content of thebubbler vessel to dispense the liquid as a vapor from the bubbler vesseland an inlet to the outlet of the bubbler vessel having a configurationselected from the group consisting of an elbow and a Tee shape, whereinat least one of the two baffle disc is solid.